The use of Langmuir-Blodgett films of a perylene derivative and polypyrrole in the detection of trace levels of Cu2+ ions

Langmuir films of a tetracarboxylic perylene derivative and polypyrrole display condensed surface pressure isotherms that are shifted when Cu2+ ions are added to the ultrapure water subphase. These films were transferred onto interdigitated gold electrodes leading to Y-type Langmuir-Blodgett (LB) films. The electrodes modified with 5-layer LB films were immersed into a flask with ultrapure water and water containing Cu2+ ions at concentrations ranging from mM to muM. Impedance measurements indicated a distinct electrical response for the two types of films. Although the materials chosen have no specificity for ionic metals, they can be combined for detecting trace levels of Cu2+, which may be exploited in water quality monitoring. (C) 2004 Elsevier B.V. All rights reserved.

HIGHER-DERIVATIVE SCHWINGER MODEL

Using the operator formalism, we obtain the bosonic representation for the free fermion field satisfying an equation of motion with higher-order derivatives. Then, we consider the operator solution of a generalized Schwinger model with higher-derivative coupling. Since the increasing of the derivative order implies the introduction of an equivalent number of extra fermionic degrees of freedom, the mass acquired by the gauge field is bigger than the one for the standard two-dimensional QED. An analysis of the problem from the functional integration point of view corroborates the findings of canonical quantization, and corrects certain results previously announced in the literature on the basis of Fujikawa's technique.

Photoconductivity excitation spectrum for stretch-oriented PPV

We have obtained the photoconductivity (PC) excitation spectrum for a stretch-oriented poly(paraphenylene vinylene) film over a wide spectral range (up to 5 eV). The measurements were performed in the surface cell configuration with the electric field parallel or perpendicular to the stretch direction. Although the sample had a stretch ratio of similar to 4, the dark conductivity and the steady-state photoconductivity were both about 40 and 20 times higher with the electric field parallel to the average chain direction, respectively. However, the shape of the PC excitation spectrum was independent of field direction and did not show a significant rise in the ultraviolet, as is usually observed for measurements in the photodiode configuration. The implications of these results to the charge photogeneration mechanism in conjugated polymers are discussed.

Spectral redistribution of waveguided emission in BEH-PPV films

We report on spectral redistribution of the photoluminescence (PL) emission from the edge of thin-film planar waveguides of the conjugated polymer BEH-PPV [Poly(2,5-bis(2'-ethyl-hexyl)-1,4-phenylenevinylene] induced by self-absorption in the polymer film. The PL spectra present drastic changes and displace to longer wavelengths with increasing self-absorption. We observe an enhancement of the absolute PL intensity at longer wavelengths, which was interpreted as due to re-emission of self-absorbed photons. The significant efficiency for the PL re-emission suggests the use of self-absorption as a mechanism for tuning the emission into the near infrared.

New higher-derivative R-4 theorems for graviton scattering

The nonminimal pure spinor formalism for the superstring is used to prove two new multiloop theorems which are related to recent higher-derivative R-4 conjectures of Green, Russo, and Vanhove. The first theorem states that when 0 < n < 12, partial derivative R-n(4) terms in the Type II effective action do not receive perturbative contributions above n/2 loops. The second theorem states that when n <= 8, perturbative contributions to partial derivative R-n(4) terms in the IIA and IIB effective actions coincide. As shown by Green, Russo, and Vanhove, these results suggest that d=4 N=8 supergravity is ultraviolet finite up to eight loops.

Effect of low contents of a polyaniline derivative on the crystallization and electrical properties of blends with PVDF

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Robust state-derivative feedback LMI-based designs for multivariable linear systems

In some practical problems, for instance in the control systems for the suppression of vibration in mechanical systems, the state-derivative signals are easier to obtain than the state signals. New necessary and sufficient linear matrix inequalities (LMI) conditions for the design of state-derivative feedback for multi-input (MI) linear systems are proposed. For multi-input/multi-output (MIMO) linear time-invariant or time-varying plants, with or without uncertainties in their parameters, the proposed methods can include in the LMI-based control designs the specifications of the decay rate, bounds on the output peak, and bounds on the state-derivative feedback matrix K. These design procedures allow new specifications and also, they consider a broader class of plants than the related results available in the literature. The LMIs, when feasible, can be efficiently solved using convex programming techniques. Practical applications illustrate the efficiency of the proposed methods.

AN ISOCOUMARIN DERIVATIVE FROM PAEPALANTHUS BROMELIOIDES

The structure of 5,7,9,10-tetramethoxy-3-methyl-1 H-naphtho[2,3-c]pyran-1-one, C18H18O6, a derivative of a natural isocoumarin isolated from Paepalanthus bromelioides, was determined by X-ray analysis, which unequivocally confirmed the previously assigned structure. Small deviations from the standard angles, resulting from steric hindrance between the methoxyl and carbonyl groups, were observed.

MEH-PPV hypsochromic shifts in halogenated solvents induced by gamma-rays

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Measurement of low-derivative surface lenses by two-laser holography with Bi12TiO20 crystals

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Methyl(2-mercapto-4-methylpyrimidinato)mercury(II): A methylmercury(II) derivative with an unusual metal-metal interaction

4-Methylpyrimidine-2-thione reacts with methylmercury hydroxide to give the thiolate derivative HgMe(SC4H2N2Me-2), the X-ray structure of which reveals pairs of molecules with a mercury-mercury distance of 3.10 Å.

Consistent higher derivative quantum field theory: A model without tachyons and ghosts

We present a higher derivative gauge theory in (2 + 1) dimensions which can have its parameters suitably tuned in order to become a consistent quantum field theory, in the sense that both tachyons and ghosts are absent from the particle spectrum of the theory.